1. Field of the Invention
The present invention relates to a concrete tunnel liner used for a shield tunneling method for a tunnel having a diameter of about 1.5 to 7.0 m; its fabrication method; and its fabrication apparatus.
2. Description of the Related Art
A tunnel liner laid around the inner surface of a tunnel having a diameter of several meters has been generally fabricated using concrete segments, concrete blocks and the like.
The tunnel liner used for a shield tunneling method requires the function that the outer surface is tightly contacted with a shield machine for preventing permeation of water.
Namely, the outer peripheral surface must be excellent in dimensional accuracy, high in water tightness, and smooth in surface finish. Such a tunnel liner is fabricated to be divided into arcuate plates, and is assembled in a cylindrical shape at a job site. Accordingly, the abutment portion between adjacent liners must be high in water tightness. To increase the water tightness, the abutment surfaces of the tunnel liners are provided with projections and grooves engaged with each other.
The arcuate plate-like concrete tunnel liner has been conventionally fabricated by a method of mounting reinforcing steelbar or coupler in a form which is stationary such that the outer peripheral surface of the tunnel liner becomes the upper surface of concrete, placing concrete in the form compacting concrete using a vibrator. The concrete liner thus fabricated has been manually finished in its upper surface of concrete.
On the other hand, there has been known a fabrication method of forming forms within a centrifugal molding drum having an inside diameter equal to the outside diameter of a tunnel liner, placing concrete in the drum, thereby centrifugally molding arcuate plate-like tunnel liners.
The tunnel liner fabricated by centrifugal molding has excellent characteristics of being compact in concrete at the outside diameter portion, high in dimensional accuracy, smooth in the surface, and superior in water tightness. However, the abutment portion between the adjacent tunnel liners has not been perfect.
Namely, in fabrication of an arcuate plate-like tunnel liner, the projections or recessed grooves provided on the surfaces of the peripheral edge of the tunnel liner are not accurately formed, and honeycomb surface is generated on the concrete surface. Moreover, micro-gaps are generated due to the inertia force of the rotation at the abutment surface of concrete with the inner surface of the form on the downstream side of the rotational direction of the centrifugal molding drum, which brings about a problem in causing the water-path on the concrete surface. The end surfaces of the peripheral edges of the liner abutting on the inner surface of the form becomes the coupling surface with the adjacent concrete liner, which are generally formed in a projection-groove engaging connection. In the worst case, there is a fear that the projection-groove engaging connection portions are broken, and the water-tightness as the most important factor of the concrete liner is lost.
The present inventors have studied a technique of dividing a tunnel liner into arcuate parts having a suitable size and centrifugally molding the divided liners particularly to enhance the water-tightness of the above abutment surface, and further of effectively fabricating a high quality tunnel liner, particularly being excellent in accuracy in the outer peripheral surface and the adjacent surface.